1. Field of the Invention
The present invention relates to wires for automatic or semi-automatic arc welding, and more particularly to an improved wire for semi-automatic arc welding with no copper plating, wherein feedability of the improved wire with no copper plating is superior to that of a solid wire with copper plating.
2. Description of the Related Art
These days, as automation or semi-automation of welding work proceeds, applications of a solid wire for gas arc welding have been significantly enlarged, particularly, in industrial fields of steel framing, automobile fabrication, shipbuilding, and building construction.
In this type of a solid wire, it is the norm that a surface of the solid wire is plated with copper to secure current-carrying characteristic and, more particularly, feedability. However, the solid wire with copper plating, which is consumed in large quantities, has the following problems, as are well known.
(a) When performing a drawing process upon manufacture of the wire, part of copper plating in the form of fine copper powder are separated from the wire, and the separated copper powder remains attached to fine prominences and depressions of the wire surface. The fine powder is then separated from the wire due to the friction between a cable or an inner sidewall of a tip and a wire, and the separated fine power is accumulated inside the tip to cause clogging, thereby deteriorating the wire feedability.
(b) Because copper is soft, the copper itself peels off due to the friction with the inner sidewall of the tip, thereby deteriorating the wire feedability.
(c) Copper is vaporized within ultrahigh temperature arc during welding and copper fumes are generated, resulting in undesirably injuring a person's health.
Methods for improving the feedability mentioned at the above (a) and (b) are proposed in Japanese Laid-open Patent Publication Nos. Heisei 1-166899, Heisei 2-284792, Heisei 7-47490, Heisei 7-223087, Heisei 7-328789, Heisei 8-197278, Heisei 9-323191, etc.
To address the feedability problem, the above-described Japanese Laid-open Patent Publications include the following processes of:                (1) coating a metal salt of a fatty acid;        (2) coating a mixture of a metal soap and oil;        (3) carrying out surface carburization, forming a crack in a carburization layer and filling the crack with a lubricant;        (4) forming artificial prominences and depressions on a surface, and filling the prominences and depressions with a lubricant;        (5) forming prominences on a wire surface, determining roughness and filling an uneven surface with a lubricant; and        (6) coating a mixture of MoS2, WS2, TiO2, etc. on the wire surface.        
The above-described processes of the above Japanese Laid-open Patent Publications cannot completely address the above-described problems (a) and (b).
To address several problems associated with the copper plating, solid wires on which the copper plating is not applied are developed.
The above-described problem (c) is addressed by not applying the copper plating on the wire, but several problems associated with the wire feedability still remain. To address the several problems associated with the wire feedability, various improved technologies are proposed, for example, in Japanese Patent No. 2682814, and Japanese Laid-open Patent Publication Nos. Heisei 11-147174, 2000-94178, 2000-317679, 2001-191195, etc. These technologies include the following processes:                (1) defining a specific surface area, coating MoS2, oil, alkali metal, etc. on the specific surface area, and simultaneously attaching materials in an amount less than 2.0 g/m2 to a surface;        (2) coating MoS2 on the wire and separating MoS2 in a weld conduit tube, thereby improving the wire feedability;        (3) forming prominences and depressions on a surface using a temporary dull finish roller and filling the prominences and depressions with MoS2, WS2, C, Na, K, Cs, etc., thereby improving the wire feedability;        (4) attaching C, TiC, WC, Al2O3, SiO2, FeO, ZnO, SnO, TiO2, FC, MoS2, BN, WS2, FeS, TiN, CrN, or SN, ZN, Cu or Fe powder together with a water soluble polymer to a wire, or coating oil on the wire, thereby improving the wire feedability (coating of insulating inorganic powder such as C, TiC, etc. and coating of conductive inorganic powder such as Sn, Zn, etc.); and        (5) defining O: 10-300 ppm, S: 0.0005-0.02%, C: 0.005-0.15%, Si: 0.2-1.2% and Mn: 1.0-2.2% contained in the wire, defining C: 0.005-3.0% detached from a wire surface based on 10 kg of a wire, defining case where Ti: 0.10-0.35% is contained in the wire or a ratio of the detached C/S+O or coating MoS2 on the wire surface, and defining a ratio of the detached C/MoS2, thereby improving the wire feedability.        
Although the above-described processes (1) to (5) are performed, the feedability of a wire with no copper plating is not superior to that of a wire with copper plating. Thus, the feedability of a wire with no copper plating should be improved.
That is, the development of technology for improving the feedability of a wire with no copper plating superior to that of a wire with copper plating, is seriously required.
The inventors of the present invention reached the conclusion that factors of roughness of a surface, a specific surface area, prominences and depressions, various coating materials, etc. in both cases of solid wires which copper plating and no copper plating be adjusted cannot improve the feedability, which is the most important characteristic of a solid wire.
Thus, as a result of carrying out detailed investigations into surface friction between a traveling wire and a conduit cable or a welding tip, the inventors of the present invention found that a solid wire with no copper plating having excellent feedability is achieved if materials capable of remarkably reducing friction are provided on an entire flat surface in a sufficient amount, because a surface of an ideal solid wire is flat like a surface of a mirror. This idea is based on the fact that complete frictionless movement of a material appears where oil is dropped on a glass surface of a mirror and then the material is put on the oil dropped on the glass.
The inventors of the present invention embodied the idea using a new method different from the conventional method through definition of microscopic characteristics of a wire surface, suitable coating material selection and the ensuring of a stable source for providing a lubricant coating material to the wire surface, and succeeded in significantly improving the feedability of a solid wire with no copper plating.